The present invention relates to a phosphor powder (phosphor crystal particle) and a production method thereof, a display panel constituted of such phosphor powders and a flat-panel display device having such a display panel.
As an image display device that can be substituted for a currently mainstream cathode ray tube (CRT), flat-type (flat-panel) display devices are studied in various ways. Such fat-panel display devices include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). There has been also proposed a cold cathode field emission display capable of emitting electrons into a vacuum from a solid without relying on thermal excitation, a so-called field emission display (FED), and it attracts attention from the viewpoint of the brightness of a display screen and low power consumption.
FIG. 4 shows a typical constitution of the cold cathode field emission display. In this cold cathode field emission display, a display panel 20 and a back panel 10 are placed so as to face each other, and these two panels 10 and 20 are bonded to each other through a frame (not shown) in their circumferential portions. A space closed with these two panels forms a vacuum space. The back panel 10 has cold cathode field emission devices (to be referred to as xe2x80x9cfield emission devicesxe2x80x9d hereinafter) as electron-emitting elements. One example shown in FIG. 4 is a so-called Spindt-type field emission device having a conical electron-emitting portion 16. The Spindt-type field emission device comprises a stripe-shaped cathode electrode 12 formed on a substrate 11; an insulating layer 13 formed on the cathode electrode 12 and the substrate 11; a stripe-shaped gate electrode 14 formed on the insulating layer 13; and a conical electron-emitting portion 16 formed in an opening portion 15 formed in the gate electrode 14 and the insulating layer 13. The electron-emitting portion 16 is formed on a portion of the cathode electrode 12 which portion is positioned in a bottom portion of the opening portion 15. Generally, a number of such electron-emitting portions 16 are formed to correspond to one of luminescent layers 22 to be described later. A relatively negative voltage (video signal) is applied to the electron-emitting portion 16 from a cathode-electrode driving circuit 31 through the cathode electrode 12, and a negatively positive voltage (scanning signal) is applied to the gate electrode 14 from a gate-electrode driving circuit 32. An electric field is generated due to the application of these voltages, and due to the electric field, electrons are emitted from the top end of the electron-emitting portion 16 on the basis of a quantum tunnel effect. The field emission device shall not be limited to the above Spindt-type field emission device, and field emission devices of other types such as plane-type, edge-type, flat-type or crown-type field emission devices are used in some cases. Further, reversibly, the scanning signal may be inputted to the cathode electrode 12, and the video signal may be inputted to the gate electrode 14.
The display panel 20 has a plurality of luminescent layers 22 which are formed on a support member 21 made of glass or the like and have the form of dots or stripes, and an anode electrode 24 made of an electrically conductive reflection film formed on the luminescent layers 22 and the support member 21. A positive voltage higher than the positive voltage applied to the gate electrode 14 is applied to the anode electrode 24 from an accelerating power source (anode-electrode driving circuit) 33, and it works to guide electrons emitted from the electron-emitting portion 16 to the vacuum space toward the luminescent layer 22. Further, the anode electrode 24 functions to protect the phosphor powders (phosphor particles) constituting the luminescent layer 22 from sputtering by particles such as ions, functions to reflect light emitted from the luminescent layers 22 on the basis of electron excitation to the side of the support member 21 to improve the brightness of a display screen observed from an outside of the support member 21, and functions to prevent excess charge to stabilize the potential of the display panel 20. That is, the anode electrode 24 not only carries out its function as an anode electrode but also carries out the function of a member known as a metal back layer in the field of a cathode ray tube (CRT). The anode electrode 24 is generally constituted of a thin aluminum film. A black matrix 23 is formed between one luminescent layer 22 and another luminescent layer 22.
FIG. 5A shows a schematic plan view of the display panel having luminescent layers 22R, 22G and 22B formed in the form of dots, and FIG. 5B shows a schematic partial cross-sectional view taken along a line Xxe2x80x94X in FIG. 5A. A region where the luminescent layers 22R, 22G and 22B are arranged is an effective field which carries out a practical function as a cold cathode field emission display, and a region where the anode electrode is formed is nearly in agreement with the effective field. For clear showing in FIG. 5A, the region where the anode electrode is formed is provided with slanting lines. A circumferential region to the effective field is an ineffective field for supporting the function of the effective field, where peripheral circuits are formed and a display screen is mechanically supported.
In the cold cathode field emission display, the anode electrode is not necessarily required to be constituted of the anode electrode 24 made of an electrically conductive reflection film as mentioned above. It may be constituted of an anode electrode 25 made of a transparent electrically conductive film formed on the support member 21, as is shown in FIG. 5C which is a schematic partial cross-sectional view similarly taken along a line Xxe2x80x94X in FIG. 5A. On the support member 21, each of the anode electrodes 24 and 25 is formed nearly on the entire surface of the effective field.
FIG. 6A shows a schematic plan view of the display panel having the luminescent layers 22R, 22G and 22B formed in the form of stripes, and FIGS. 6B and 6C show schematic partial cross-sectional views taken along a line Xxe2x80x94X in FIG. 6A. In FIGS. 6A, 6B and 6C, the same portions as those in FIGS. 5A, 5B and 5C are shown by the same reference numerals, and detailed explanations of the same portions are omitted. FIG. 6B shows a constitution in which the anode electrode 24 is made of an electrically conductive reflection film, and FIG. 6C shows a constitution in which the anode electrode 25 is made of a transparent electrically conductive film. Each of the anode electrodes 24 and 25 is formed nearly on the entire surface of the effective field of the display panel.
In the cold cathode field emission display that is a flat-panel display device, the flying distance of electrons is far smaller than the counterpart in a cathode ray tube, so that it is difficult to increase an electron-accelerating voltage to the level of an electron-accelerating voltage in the cathode ray tube. In the cold cathode field emission display, if the electron-accelerating voltage is too high, spark discharge is liable to take place between the gate electrode or the electron-emitting portion in the back panel and the anode electrode provided in the display panel, and the display quality may be impaired to a great extent. The accelerating voltage is therefore controlled to be approximately 10 kilovolts or lower.
In addition to the above problem, the cold cathode field emission display for which it is required to select the above low electron-accelerating voltage involves characteristic problems from which the cathode ray tube is free. In a cathode ray tube permitting the acceleration at a high voltage, electrons enter the luminescent layer deep, so that the electron energy is received in a relatively broad region inside the luminescent layer to excite a relatively large number of phosphor powders present in such a broad region at once, and high luminescence efficiency can be attained. When the accelerating voltage is set at 31.5 kilovolts and when the luminescent layer is made of ZnS, Monte Carlo simulation is conducted with regard to a relationship between an energy loss of electrons which have entered the luminescent layer and the electron penetration depth into the luminescent layer on the basis of the Bethe expression represented by the following equation (1) (see xe2x80x9cPractical Scanning Electron Microscopyxe2x80x9d, J. I. Goldstein and H. Yokowitz, p 50, Plenun Press, New York (1975)). FIG. 20 shows the result thereof. It is seen from FIG. 20 that when the accelerating voltage is 31.5 kilovolts, the peak of electron energy loss is positioned approximately 1 xcexcm apart from the surface of the luminescent layer. Further, electrons enter approximately 5 xcexcm deep from the surface of the luminescent layer. In the simulation, it is assumed that electrons lose approximately 43 eV in average (mean free path: approximately 4.8 nm) due to one scattering, and they stop after they suffer elastic scatterings approximately 150 times in average.
xe2x80x83xe2x88x92(dEm/dX)=2xcfx80e4N0(Z/A)(xcfx81/Em)ln(1.166Em/J)xe2x80x83xe2x80x83(1)
In the cold cathode field emission display, however, the accelerating voltage is required to be approximately 10 kilovolts or lower, for example, approximately 6 kilovolts. When the accelerating voltage is set at 6 kilovolts and when the luminescent layer is made of ZnS, Monte Carlo simulation is conducted with regard to a relationship between an energy loss of electrons which have entered the luminescent layer and the electron penetration depth into the luminescent layer on the basis of the above Bethe expression, and FIGS. 21 and 22 show the results. In FIG. 21, it is assumed that a 0.045 xcexcm thick aluminum thin film is formed on the surface of the luminescent layer, and in FIG. 22, it is assumed that a 0.07 xcexcm thick aluminum thin film is formed on the surface of the luminescent layer. FIGS. 21 and 22 show that the peak of electron energy loss is positioned near the outermost surface of the luminescent layer. Further, electrons enter only approximately 0.2 to 0.3 xcexcm deep from the surface of the luminescent layer. In the cold cathode field emission display in which the accelerating voltage is lower than that in the cathode ray tube, the electron penetration depth into the luminescent layer is small, and the electron energy can be received only in a narrow region of the luminescent layer (particularly, only near the surface of the luminescent layer).
In the luminescent layer, further, approximately 10% of the energy of electrons contributes to light emission, and the remaining approximately 90% of the energy is converted to heat. That is, heat is generated greatly near the surface of the luminescent layer. As a result, when the luminescent layer is constituted of phosphor powders made of a sulfide, sulfur that is a component therefore is dissociated in the form of a single atom or in the form of sulfur monoxide (SO) or sulfur dioxide (SO2), and the phosphor powders made of a sulfide alter in composition or a luminescence center disappears. When the accelerating voltage is set at 6 kilovolts and when the luminescent layer is made of ZnS, Monte Carlo simulation is conducted with regard to a relationship between an energy loss of electrons which have entered the luminescent layer and the electron penetration depth into the luminescent layer on the basis of the above Bethe expression, and FIG. 23 shows the result thereof. In FIG. 23, it is assumed that a 0.07 xcexcm thick aluminum thin film is formed on the surface of the luminescent layer and that Zn is formed due to dissociation of sulfur (S) from ZnS in a thickness ranging from the surface of the luminescent layer to a portion approximately 0.03 xcexcm deep from the surface. FIG. 23 clearly shows that the peak of electron energy loss is positioned in a region of the luminescent layer which region is made of Zn due to the dissociation of sulfur (S) from ZnS. Further, electrons reach only approximately 0.2 xcexcm deep from the surface of the luminescent layer.
In the cold cathode field emission display, further, the position in the luminescent layer (more specifically, phosphor powders) with which position electrons emitted from one field emission device collide is generally constant unlike the cathode ray tube. Therefore, the phosphor powders with which the electrons collide constantly is deteriorated greatly as compared with other phosphor powders, and the phosphor powders are deteriorated faster that the counterpart in the cathode ray tube.
Further, the outermost surface of the phosphor powder suffers various strains during the processes of producing the phosphor powders and producing the display panel and is liable to have lattice defects. Moreover, it is required to drive the cold cathode field emission display at a higher current density (emitted-electron density) than the cathode ray tube for attaining desired luminescence efficiency. For example, a current density in the cathode ray tube is 0.1 to 1 xcexcA/cm2, while the cold cathode field emission display requires a current density of as high as 5 to 10 xcexcA/cm2. It is therefore required to operate the outermost surface of the phosphor powder or a portion nearby under high-excitation conditions. While the cold cathode field emission display is operated, crystal defects are liable to be formed or multiplied newly in the phosphor powder, which is considered to cause the deterioration of the luminescence efficiency to proceed faster.
The above-explained deterioration of the luminescent layer or the phosphor powders results in the fluctuation of emitted-light color and luminescence efficiency, the contamination of internal components of the cold cathode field emission display and a consequent decrease in reliability and lifetime characteristics of the cold cathode field emission display. It is therefore strongly desired to develop a luminescent layer or phosphor powders free from deterioration, that is, free from crystal defects, for improving the cold cathode field emission display in reliability and lifetime characteristics.
For attaining finer display with a cathode ray tube, it is required to decrease a diameter of an electron beam that collides with the luminescent layer. That is, it is required to increase the current density of the electron beam that collides with the luminescent layer. In this method, however, the phosphor powders that emit light in green are particularly liable to be damaged, and such a phenomenon leads to the generation of a magenta ring. The above magenta ring refers to a phenomenon in which the phosphor powders that emit light in red and light in blue are scarcely damaged, and in the cathode ray tube, a magenta color that is a complementary color to green is observed in the form of a ring. In the conventional cathode ray tube, the current density of the electron beam that collides with the luminescent layer and the lifetime of the cathode ray tube are inversely proportional to each other. For preventing a decrease in the lifetime of the cathode ray tube while increasing the current density of the electron beam that collides with the luminescent layer, it is strongly desired to develop a luminescent layer or phosphor powders which is/are deteriorated to a less degree, that is, has/have crystal defects to a less degree.
It is therefore an object of the present invention to provide phosphor powders that have crystal defects to a less degree and are deteriorated to a less degree even in use for a long period of time, namely, that suffer a decrease in luminescence efficiency to a less degree, a display panel constituted of such phosphor powders, and a flat-panel display device provided with such a display panel.
The phosphor powder according to a first aspect of the present invention for achieving the above object is a phosphor powder composed of a host material made of an element coming under the group II of the periodic table and an element coming under the group VI of the periodic table, an activator and a co-activator,
wherein the amount ratio of the activator to the host material is 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x923 parts by weight when the amount ratio of the host material is 1 part by weight, and the co-activator has a molar concentration equal to a molar concentration of the activator.
The display panel according to a first aspect of the present invention for achieving the above object is a display panel comprising a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying through a vacuum space, and an electrode,
wherein said phosphor powder is composed of a host material made of an element coming under the group II of the periodic table and an element coming under the group VI of the periodic table, an activator and a co-activator, and
the amount ratio of the activator to the host material is 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x923 parts by weight when the amount ratio of the host material is 1 part by weight, and the co-activator has a molar concentration equal to a molar concentration of the activator.
The flat-panel display device according to a first aspect of the present invention for achieving the above object is a flat-panel display device comprising a display panel and a back panel having a plurality of electron emitting regions, the display panel and the back panel being disposed to face each other through a vacuum space interposed therebetween,
wherein the display panel comprises a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying from the electron emitting region, and an electrode,
said phosphor powder is composed of a host material made of an element coming under the group II of the periodic table and an element coming under the group VI of the periodic table, an activator and a co-activator, and
the amount ratio of the activator to the host material is 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x923 parts by weight when the amount ratio of the host material is 1 part by weight, and the co-activator has a molar concentration equal to a molar concentration of the activator.
The phosphor powder, the display panel and the flat-type display device according to the first aspect of the present invention will be generically simply referred to as xe2x80x9cfirst aspect of the present inventionxe2x80x9d for convenience hereinafter.
In the first aspect of the present invention, the amount ratio of the activator (corresponding to an acceptor in the field of semiconductor technology) is defined, whereby a number of light emission centers can be therefore provided, so that effective light emission can be attained. Further, it is also made possible to avoid a problem that the amount of impurities that do not contribute to light emission increases and that a concentration extinction that is to decrease activation efficiency may take place. Further, the molar concentration of the co-activator (corresponding to a donor in the filed of semiconductor technology) is arranged to be equal to the molar concentration of the activator, whereby remarkably high light emission efficiency can be obtained. In addition, the amount ratio of the activator is defined, and the molar concentration of the co-activator is arranged to be equal to the molar concentration of the activator, whereby a phosphor powder obtained is improved in crystallinity, and there can be obtained a phosphor powder that does not much deteriorate in the continuous use for a long period of time, that is, which does not much decrease in luminescence efficiency.
The activator and the co-activator can be measured for their amount ratios by chemical analysis, for example, atomic absorption analysis.
The phosphor powder according to a second aspect of the present invention for achieving the above object is a phosphor powder having a surface free of a topmost-surface crystal-lattice-defect layer or a surface-damaged layer.
The display panel according to a second aspect of the present invention for achieving the above object is a display panel comprising a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying through a vacuum space, and an electrode,
wherein said phosphor powder has a surface free of a topmost-surface crystal-lattice-defect layer or a surface-damaged layer.
The flat-panel display device according to a second aspect of the present invention for achieving the above object is a flat-panel display device comprising a display panel and a back panel having a plurality of electron emitting regions, the display panel and the back panel being disposed to face each other through a vacuum space interposed therebetween,
wherein the display panel comprises a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying from the electron emitting region, and an electrode, and
said phosphor powder has a surface free of a topmost-surface crystal-lattice-defect layer or a surface-damaged layer.
The phosphor powder, the display panel and the flat-type display device according to the second aspect of the present invention will be generically simply referred to as xe2x80x9csecond aspect of the present inventionxe2x80x9d for convenience hereinafter.
In the second aspect of the present invention, the topmost-surface crystal-lattice-defect layer or the surface-damaged layer is removed from the surface of the phosphor powder, so that a phosphor powder obtained is improved in crystallinity, and there can be obtained a phosphor powder that does not much deteriorate in the continuous use for a long period of time, that is, which does not much decrease in luminescence efficiency.
By preparing a laminar sample of cross section of the phosphor powder and observing the laminar sample for a bright field image and a lattice image through a transmission electron microscope, it can be inspected whether or not the topmost-surface crystal-lattice-defect layer or the surface-damaged layer is removed from the surface of the phosphor powder.
The phosphor powder according to a third aspect of the present invention for achieving the above object is a phosphor powder having a surface coated with a chemical-reaction layer containing phosphoric acid.
The display panel according to a third aspect of the present invention for achieving the above object is a display panel comprising a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying through a vacuum space, and an electrode,
wherein said phosphor powder has a surface coated with a chemical-reaction layer containing phosphoric acid.
The flat-panel display device according to a third aspect of the present invention for achieving the above object is a flat-panel display device comprising a display panel and a back panel having a plurality of electron emitting regions, the display panel and the back panel being disposed to face each other through a vacuum space interposed therebetween,
wherein the display panel comprises a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying from the electron emitting region, and an electrode, and
said phosphor powder has a surface coated with a chemical-reaction layer containing phosphoric acid.
The phosphor powder, the display panel and the flat-type display device according to the third aspect of the present invention will be generically simply referred to as xe2x80x9cthird aspect of the present inventionxe2x80x9d for convenience hereinafter.
In the third aspect of the present invention, the average thickness of the chemical-reaction layer is desirably 1 nm to 5 nm. When the average thickness of the chemical-reaction layer is too large, light transmitted from the phosphor powder may be absorbed by the chemical-reaction layer. Desirably, the chemical-reaction layer has a thickness that is as uniform as possible. The chemical-reaction layer can be formed in the surface-treatment step in a production method of a phosphor powder to be described later. The chemical-reaction layer is preferably made of zinc phosphate or calcium phosphate.
As a surface treatment of a phosphor powder, conventionally, there has been employed a method in which silica is allowed to adhere to the surface of a phosphor powder by a sol-gel method or a method in which a powdered silica is allowed to adhere to the surface of a phosphor powder. According to studies made by the present inventor, it has been found that when a phosphor powder is irradiated with energy flux, the silica is decomposed and a crystal in the surface of the phosphor powder to which the silica has adhered is caused to have a defect. It is considered that when the chemical-reaction layer containing phosphoric acid is formed on the phosphor powder, the chemical-reaction layer undergoes a kind of epitaxial growth on the surface of the phosphor powder, and a crystal lattice defect does not easily occur on the surface of the phosphor powder due to the formation of the chemical-reaction layer, so that the phosphor powder is improved in crystallinity. Further, damage does not easily occur in the chemical-reaction layer even under irradiation with energy flux, so that there can be obtained a phosphor powder that does not easily deteriorate in continuous use for a long period of time, that is, which does not easily decrease in luminescence efficiency.
By preparing a laminar sample of cross section of the phosphor powder and observing the laminar sample for a bright field image and a lattice image through a transmission electron microscope, it can be inspected whether or not the chemical-reaction layer is formed on the surface of the phosphor powder. The layer thickness can be also measured by the same method.
The phosphor powder according to a fourth aspect of the present invention for achieving the above object is a phosphor powder having a temperature T50 of at least 200xc2x0 C., the temperature T50 being a temperature at which a luminescence efficiency reaches xc2xd of a luminescence efficiency at 25xc2x0 C. in a thermal quenching performance.
The display panel according to a fourth aspect of the present invention for achieving the above object is a display panel comprising a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying through a vacuum space, and an electrode,
wherein said phosphor powder has a temperature T50 of at least 200xc2x0 C., the temperature T50 being a temperature at which a luminescence efficiency reaches xc2xd of a luminescence efficiency at 25xc2x0 C. in a thermal quenching performance.
The flat-panel display device according to a fourth aspect of the present invention for achieving the above object is a flat-panel display device comprising a display panel and a back panel having a plurality of electron emitting regions, the display panel and the back panel being disposed to face each other through a vacuum space interposed therebetween,
wherein the display panel comprises a support member, a luminescent layer made of phosphor powders which emit light upon irradiation with electrons that come flying from the electron emitting region, and an electrode, and
said phosphor powder has a temperature T50 of at least 200xc2x0 C., the temperature T50 being a temperature at which a luminescence efficiency reaches xc2xd of a luminescence efficiency at 25xc2x0 C. in a thermal quenching performance.
The phosphor powder, the display panel and the flat-type display device according to the fourth aspect of the present invention will be generically simply referred to as xe2x80x9cfourth aspect of the present inventionxe2x80x9d for convenience hereinafter.
In the fourth aspect of the present invention, desirably, the temperature T50 is at least 200xc2x0 C., preferably at least 250xc2x0 C., still more preferably at least 350xc2x0 C., yet more preferably at least 400xc2x0 C.
In the fourth aspect of the present invention, the temperature T50 is defined, so that there can be obtained a phosphor powder improved in crystallinity and that there can be obtained a phosphor powder that does not easily deteriorate in continuous use for a long period of time, that is, which does not easily decrease in luminescence efficiency.
The above thermal quenching performance of the phosphor powder is called xe2x80x9ctemperature extinction characteristicxe2x80x9d. A phosphor powder is measured for luminescence efficiency at 25xc2x0 C. (initial value of luminescence efficiency), the phosphor powder is measured for luminescence efficiency while the phosphor powder is heated, and the temperature T50 can be determined on the basis of measurement results of such luminescence efficiency characteristics of the phosphor powder to temperature. In the actual continuous use of the phosphor powder for a long period of time, the initial value of the luminescence efficiency before measurement is restored when the temperature is brought back to 25xc2x0 C.
In the phosphor powder according to the first to fourth aspects of the present invention, the phosphor powder includes a phosphor powder composition formed by dispersing, in a dispersing agent, the phosphor powder specified in any one of these embodiments.
The phosphor powder in the preferred embodiment of any one of the second to fourth aspects of the present invention or a phosphor powder obtained by a production method of a phosphor powder according to first to third aspects of the present invention to be described later comprises a host material (core material) made of elements coming under the groups II-VI of the periodic table, an activator and a co-activator, and when the amount ratio of the host material is 1 part by weight, preferably, the amount ratio of the activator is 1xc3x9710xe2x88x924 part by weight (100 ppm) to 1xc3x9710xe2x88x923 part by weight (1000 ppm), and the molar concentration of the co-activator is equal to the molar concentration of the activator. In this case, or in the first aspect of the present invention, when the amount ratio of the host material is 1 part by weight, desirably, the amount ratio of the activator is preferably 3xc3x9710xe2x88x924 part by weight (300 ppm) to 8xc3x9710xe2x88x924 part by weight (800 ppm), still more preferably 5xc3x9710xe2x88x924 part by weight (500 ppm) to 6xc3x9710xe2x88x924 part by weight (600 ppm). When the amount ratio of the activator is less than 1xc3x9710xe2x88x924 part by weight, a number of light emission centers is too small, and it is difficult to cause light emission. When the amount ratio of the activator exceeds 1xc3x9710xe2x88x923 part by weight, the amount of impurities that do not contribute to light emission increases, and the concentration extinction that is to decrease activation efficiency may take place. That the molar concentration of the co-activator is equal to the molar concentration of the activator, that is, that the number of atoms (atomic %) of the co-activator is equal to the number of atoms (atomic %) of the activator means that when the molar concentration of the activator is 1.00, the molar concentration of the co-activator is brought close to 0.95 to 1.05, preferably to 0.98 to 1.02, more preferably to as close as 1.00.
In the phosphor powder in the preferred embodiments of the second to fourth aspects of the present invention, and, further, in the production method of a phosphor powder according to the first to third aspects of the present invention to be described later, when the host material (core material) is made of elements coming under the groups II-VI of the periodic table, or in the first aspect of the present invention, there may be employed a constitution in which the elements for constituting the host material are zinc (Zn) and sulfur (S), the element for constituting the activator is silver (Ag), and the element for constituting the co-activator is aluminum (Al). The above phosphor powder emits light in blue. Alternatively, there may be employed a constitution in which the elements for constituting the host material are zinc (Zn) and sulfur (S), the element for constituting the activator is copper (Cu), and the element for constituting the co-activator is aluminum (Al). The above phosphor powder emits light in green.
The group II element for constituting the host material includes cadmium (Cd) in addition to zinc (Zn), and the group VI element includes selenium (Se) and tellurium (Te) in addition to sulfur (S). That is, the combination of the elements of II-VI groups for constituting the host material includes (Zn/S), (Zn/Se), (Zn/Te), (Zn/S,Se), (Zn/S,Te), (Zn/Se,Te), (Zn/S,Se,Te), (Cd/S), (Cd/Se), (Cd/Te), (Cd/S,Se), (Cd/S,Te), (Cd/Se,Te), (Cd/S,Se,Te), (Zn,Cd/S), (Zn,Cd/Se), (Zn,Cd/Te), (Zn,Cd/S,Se), (Zn,Cd/S,Te), (Zn,Cd/Se,Te) and (Zn,Cd/S,Se,Te).
The activator includes gold (Au) in addition to silver (Ag) and copper (Cu). In this case, the phosphor powder emits light in green. Further, the co-activator includes gallium (Ga) and indium (In) in addition to aluminum (Al).
As specific examples of the phosphor powder in the first aspect of the present invention, as specific examples of the phosphor powder in the preferred embodiments of the second to fourth aspects of the present invention, or as specific examples of the phosphor powder produced by the production method of a phosphor powder according to the first to third aspects of the present invention to be described later, the phosphor powder that emits light in blue includes [ZnS:Ag,Al] and [ZnS:Ag,Ga], the phosphor powder that emits light in green includes [ZnS:Cu,Al], [ZnS:Cu,Au,Al], [(Zn,Cd)S:Cu,Al], [(Zn,Cd)S:Ag,Al] and [Zn(S,Se):Ag,Al].
Further, as specific examples of the phosphor powder according to the second to fourth aspects of the present invention, or as specific examples of the phosphor powder produced by the production method of a phosphor powder according to the first to third aspects of the present invention to be described later, the phosphor powder that emits light in blue includes the above phosphor powders and also includes [ZnS:Ag], and the phosphor powder that emits light in green includes [Zn2SiO4:Mn2+], [(Zn,Cd)S;Ag] and [(Zn,Cd)S:Cu]. Further, the phosphor powder that emits light in red includes [Zn3(PO4)2:Mn2+], [(Zn,Cd)S:Ag], [YVO4:Eu3+], [Y2O2S:Eu3+] and [Y2O3:Eu3+]. Further, the phosphor powder that emits light in reddish orange includes [Y2O2S:Eu3+], and the phosphor powder that emits light in violet-blue includes [ZnS;Ag].
In the first to fourth aspects of the present invention, preferably, the chlorine concentration of a chlorine-containing compound (for example, NaCl) contained in the phosphor powder is not more than 20 ppm, or a detection limit of a measuring apparatus or less. The above chlorine-containing compound is used for decreasing the firing temperature in the firing step in the production method of a phosphor powder to be described later, and it is added in the step of mixing the host material with the activator and the co-activator. When the chlorine concentration of the chlorine-containing compound contained in the phosphor powder is too high, the crystallinity of the phosphor powder may decrease, so that the chlorine concentration is desirably of the above value or less.
The third aspect of the present invention can be combined with the second aspect of the present invention. That is, there can be employed a constitution in which the topmost-surface crystal-lattice-defect layer or the surface-damaged layer is removed from the surface of the phosphor powder immediately below the chemical-reaction layer. Alternatively, the fourth aspect of the present invention can be combined with the second aspect of the present invention. That is, there can be employed a constitution in which the topmost-surface crystal-lattice-defect layer or the surface-damaged layer is removed from the surface of the phosphor powder. Alternatively, the fourth aspect of the present invention can be combined with the third aspect of the present invention. That is, there can be employed a constitution in which the surface of the phosphor powder is coated with the chemical-reaction layer containing phosphoric acid.
The production method of a phosphor powder according to a first aspect of the present invention (to be sometimes referred to as xe2x80x9cfirst aspect of the production method according to the present invention) is a production method which comprises preparing a host material by a solution-preparation step and a reaction step, then, mixing the host material with an activator and a co-activator, and then carrying out a firing step and a surface-treatment step, and
the production method further comprises a removal step of removing a topmost-surface crystal-lattice-defect layer or a surface-damaged layer formed in the surface of the firing product between the firing step and the surface-treatment step.
In the production method according to the first aspect of the present invention, the topmost-surface crystal-lattice-defect layer or the surface-damaged layer is removed from the surface of the phosphor powder, so that the phosphor powder is improved in crystallinity, and that there can be obtained a phosphor powder that does not much deteriorate for a continuous use for a long period of time, that is, which does not much decrease in luminescence efficiency.
In the production method according to the first aspect of the present invention, the removal step can comprise an annealing treatment or an etching treatment. The temperature in the above annealing treatment is desirably lower than the firing temperature in the firing step. Further, the annealing treatment is preferably carried out in a reducing atmosphere or an inert gas atmosphere, from the viewpoint of preventing the oxidation of the phosphor powder. Otherwise, in the etching treatment, it is desirable to use, as an etching solution, a solution prepared by mixing a persaturated solution consisting of phosphoric acid (for example, hot phosphoric acid at 60xc2x0 C.) into which CrO3 is added, with concentrated hydrochloric acid in the persaturated solution:the concentrated hydrochloric acid mixing ratio of 1:2.
In the production method according to the first aspect of the present invention, preferably, a washing step is provided between the firing step and the removal step, and the firing product is washed such that the chlorine concentration of the chlorine-containing compound (for example, NaCl) contained in the phosphor powder is not more than 20 ppm, or a detection limit of a measuring apparatus or less. By the above procedure, the phosphor powder can be improved in crystallinity. In the surface-treatment step, preferably, the surface of the phosphor powder is coated with a chemical-reaction layer containing phosphoric acid. The chemical-reaction layer preferably has an average thickness of 1 nm to 5 nm, and further, the chemical-reaction layer is preferably made of zinc phosphate or calcium phosphate, whereby the phosphor powder can be also improved in crystallinity. For coating the surface of the phosphor powder with the chemical-reaction layer containing phosphoric acid, for example, a solution of a compound containing phosphoric acid is prepared, and the phosphor powder is immersed in the solution and then dried. The above description is also applicable to the production method of a phosphor powder according to the second or third aspect of the present invention to be described below.
The production method of a phosphor powder according to a second aspect of the present invention (to be sometimes referred to as xe2x80x9csecond aspect of the production method according to the present invention) is a production method which comprises preparing a host material by a solution-preparation step and a reaction step, then, mixing the host material with an activator and a co-activator, and then carrying out a firing step and a surface-treatment step,
wherein the firing step is followed by a washing step, and the firing product is washed so that a chlorine-containing compound contained in the phosphor powder has a chlorine concentration of 20 ppm or less.
In the production method according to the second aspect of the present invention, preferably, the surface of the phosphor powder is coated with a chemical-reaction layer containing phosphoric acid in the surface-treatment step.
The production method of a phosphor powder according to a third aspect of the present invention (to be sometimes referred to as xe2x80x9cthird aspect of the production method according to the present invention) is a production method which comprises preparing a host material by a solution-preparation step and a reaction step, then, mixing the host material with an activator and a co-activator, and then carrying out a firing step and a surface-treatment step,
wherein the surface of the phosphor powder is coated with a chemical-reaction layer containing phosphoric acid in the surface-treatment step.
The phosphor powders of the present invention can be used for constituting, for example, a cold cathode field emission display or the front panel (anode panel) thereof; a commercial (home-use), industrial (for example, a computer display), digital broadcasting or projection type cathode ray tube or a face plate thereof; or a plasma display or a rear panel thereof. The rear panel for an AC driven or DC driven plasma display comprises, for example, a support member; separation walls (ribs) formed on the support member; various electrodes (for example, data electrode) formed on the support member located between one separation wall and another separation wall; and a luminescent layer made of the phosphor powders formed between one separation wall and another separation wall. The front panel (anode panel) of the cold cathode field emission display and the face plate of the cathode ray tube will be discussed later.
The display panel of the present invention includes a so-called face plate of a commercial (home-use), industrial (for example, computer display), digital broadcasting or projection type cathode ray tube; or a front panel (anode panel) for a cold cathode field emission display. The face plate for a cathode ray tube generally comprises a glass panel (corresponding to the support member in the display panel of the present invention) and phosphor powders, and has luminescent layers formed on an inner surface of the glass panel in the form of stripes or dots; a black matrix formed on the inner surface of the glass panel between one luminescent layer and another luminescent layer; and a metal back layer (corresponding to the electrode in the display panel of the present invention) formed on the luminescent layers and the black matrix. The front panel (anode panel) of a cold cathode field emission display comprises a support member; luminescent layers made of the phosphor powders and formed in the form of stripes or dots (luminescent layers which are patterned in the form of stripes or dots, correspond to three primary colors, red (R), green (G) and blue (B), and are alternately arranged for a color display); and an anode electrode (corresponding to the electrode in the display panel of the present invention). A black matrix may be formed between one luminescent layer and another luminescent layer.
The display panel of the flat-type display device of the present invention includes the above-mentioned a front panel (anode panel) for a cold cathode field emission display. The cold cathode field emission display will be discussed later.
In the display panel of the present invention or the display panel of the flat-panel display device of the present invention, the luminescent layer can be formed by a screen printing method or a slurry method. In the screen printing method, the phosphor powder composition is printed on the support member (on the electrode and the support member in some cases), the applied composition is dried and fired, whereby the luminescent layer can be formed. In the slurry method, the phosphor powder composition containing a photosensitive polymer and being in the state of a slurry is applied to the support member (to the electrode and the support member in some cases) to form a coating film, and then, the photosensitive polymer is insolubilized to a developer solution by exposure to light, whereby the luminescent layer can be formed. For displaying three primary colors of (R,G,B), three phosphor powder compositions or three slurries are consecutively used, and the luminescent layers for emitting light in such three colors can be formed by the screen printing method or the slurry method.
In the phosphor powder composition, water can be used as a dispersing medium. The phosphor powder composition may contain polyvinyl alcohol as a dispersing agent or a retaining agent, and ammonium bichromate may be used as a photosensitive polymer. The phosphor powders of the present invention may be surface-treated on their manufacturing process, for improving the dispersing property and adhesion thereof.
An electron beam can be used as an energy beam for making the phosphor powders of the present invention emit light. The energy of the electron beam for irradiation of the phosphor powders is preferably set at 0.5 keV to 35 keV. In the above constitution, specifically, the phosphor powders can be used for constituting a cold cathode field emission display or a front panel (anode panel) thereof; or a commercial (home-use), industrial (for example, computer display), digital broadcasting or projection type cathode ray tube or a face plate thereof. Otherwise, there may be employed a constitution in which the energy of the electron beam for irradiation of the phosphor powders is 0.5 keV to 10 keV and the electron penetration depth from the surface of the phosphor powder is 0.5 xcexcm or less. In the above constitution, specifically, the phosphor powders can be used for constituting a cold cathode field emission display or a front panel (anode panel) therefore. Otherwise, in the phosphor powders of the present invention, an ultraviolet ray can be used as an energy beam. In this case, preferably, the ultraviolet ray for irradiation of the phosphor powders has a wavelength of 100 nm to 400 nm. In the above constitution, specifically, the phosphor powders can be used for constituting a plasma display or a rear panel therefore.
When the flat-type display device of the present invention is constituted of a cold cathode field emission display, the material for constituting the anode electrode corresponding to the electrode can be properly selected depending upon the constitution of the cold cathode field emission display. That is, when the cold cathode field emission display is a transmission type (the display panel corresponds to a display screen), and when the anode electrode and the luminescent layer are stacked on the support member in this order, not only the support member but also the anode electrode itself is required to be transparent, and a transparent electrically conductive material such as indium-tin oxide (ITO) is used. When the cold cathode field emission display is a reflection type (the back panel corresponds to a display screen), or when the cold cathode field emission display is a transmission type and the luminescent layer and the anode electrode are stacked on the support member in this order, ITO can be used, and besides ITO, the material for the anode electrode can be properly selected from materials to be discussed later with respect of a cathode electrode or a gate electrode. When the anode electrode is constituted of aluminum (Al) or chromium (Cr), for example, the specific thickness of the anode electrode is 3xc3x9710xe2x88x928 m (30 nm) to 1.5xc3x9710xe2x88x927 m (150 nm), preferably 5xc3x9710xe2x88x928 m (50 nm) to 1xc3x9710xe2x88x927 m (100 nm). The anode electrode can be formed by a vapor deposition method or a sputtering method. The anode electrode may be an anode electrode having a form in which the effective field is covered with one sheet-shaped electrically conductive material or may be an anode electrode having a form in which anode electrode units each of which corresponds to one or a plurality of electron-emitting portions or one or a plurality of pixels are gathered. When the anode electrode has the former constitution, the anode electrode can be connected to the anode-electrode driving circuit. When the anode electrode has the latter constitution, for example, each anode electrode unit can be connected to the anode-electrode driving circuit. Examples of the constitution of the anode electrode and the luminescent layer include a constitution (1) in which the anode electrode is formed on the support member and the luminescent layer is formed on the anode electrode, and a constitution (2) in which the luminescent layer is formed on the support member and the anode electrode is formed on the luminescent layer. In the constitution (1), a so-called metal back film electrically connected to the anode electrode may be formed on the luminescent layer. In the constitution (2), a metal back layer may be formed on the anode electrode.
When the flat-type display device of the present invention is a cold cathode field emission display, or when the display panel of the present invention is the front panel (anode panel) of a cold cathode field emission display, ribs may be formed on the support member for preventing the occurrence of a so-called optical crosstalk, that is, electrons which collide with the luminescent layer are scattered backward and again collide with an adjacent luminescent layer to cause the adjacent luminescent layer to emit light. When the optical crosstalk occurs, a useless color is mixed with a color of light that should be emitted, so that the chromaticity decreases. With an increase in the acceleration voltage of electrons, the electrons are scattered backward to a greater extent. Therefore, desirably, the height of the ribs is determined by not only taking account of the thickness of the luminescent layer but also taking account of the backward scattering of electrons. The material for constituting the above ribs can be selected from known insulating materials, such as metal oxides, low melting glass or a material prepared by mixing low melting glass with a metal oxide such as alumina.
Examples of the method of forming the ribs include a screen printing method, a sand blasting method, a dry film method and a photo-sensitive method. The screen printing method refers to a method in which a screen has openings in its portions corresponding to the ribs to be formed, a rib-forming material on the screen is allowed to pass the openings with a squeezer to form rib-forming material layer on the support member, and the rib-forming material layer is calcined or sintered. The sand blasting method refers to a method in which a rib-forming material layer is formed on the support member, for example, by screen printing or with a roll coater, a doctor blade or a nozzle ejection coater, the formed rib-forming material layer is dried and then masked with a mask layer in portions where the ribs are to be formed, and then the exposed portions of the rib-forming material layer are removed by a sand blast method. The dry film method refers to a method in which a photosensitive film is laminated on the support member, the portions of the photosensitive film where the ribs are to be formed are removed by exposure and development, opening portions formed by the removal are filled with an insulating material layer, and the insulating material layer is calcined or sintered. The photosensitive film is combusted and removed by calcining or sintering, and the rib-forming insulating material layer filled in the opening portions remains and constitutes the ribs. The photo-sensitive method refers to a method in which a photosensitive rib-forming insulating material layer is formed on the support member, and the insulating material layer is patterned by exposure and development and then calcined or sintered. The material for constituting the ribs can be selected from known electrically conductive materials. In this case, the ribs can be formed by a plating method based on an electrically conductive material. The formed ribs may be polished to flatten the top surface of each rib. In the cold cathode field emission display, the front panel (anode panel) and the back panel (cathode panel) have a high vacuum in a space between them. Therefore, when no spacer is provided between the front panel (anode panel) and the back panel (cathode panel), the cold cathode field emission display may be damaged due to atmospheric pressure. The ribs in some cases work as a spacer holding portion for holding the spacer.
The form of the ribs includes the form of a lattice (grilles), that is, a form in which the rib surrounds the luminescent layer having a plan form of a nearly rectangle (or dot-shaped), and a stripe or band-like form that extends in parallel with opposite two sides of a rectangular or stripe-shaped luminescent layer. When the rib(s) have the form of a lattice, the rib may have a form in which the rib continuously or discontinuously surrounds four sides of one luminescent layer. When the rib(s) has the form of a stripe, the stripe may be continuous or discontinuous.
For improving the contrast of display images, preferably, a black matrix that absorbs light from the luminescent layer is formed between one luminescent layer and another adjacent luminescent layer and between the rib and the support member. As a material for constituting the black matrix, it is preferred to select a material that absorbs at least 99% of light from the luminescent layer. The above material includes carbon, a thin metal film (made, for example, of chromium, nickel, aluminum, molybdenum and an alloy of these), a metal oxide (for example, chromium oxide), metal nitride (for example, chromium nitride), a heat-resistant organic resin, a glass paste, and a paste containing a black pigment or electrically conductive particles of silver or the like. Specific examples thereof include a photosensitive polyimide resin, chromium oxide and a chromium oxide/chromium stacked film. Concerning the chromium oxide/chromium stacked film, the chromium film is to be in contact with the support member.
In the flat-type display device of the present invention, the substrate constituting the back panel or the support member constituting the display panel may be any substrate or any support member so long as they have a surface constituted of an insulating member. Examples of the substrate or the support member include various glass substrates such as an alkali-free glass substrate, a low-alkali glass substrate and a quartz glass substrate; a various glass substrates on which surface an insulating layer is formed; a quartz substrate; a quartz substrate on which surface an insulating layer is formed; and a semiconductor substrate on which surface an insulating layer is formed. From the viewpoint of decreasing a production cost, it is preferred to use a glass substrate or a glass substrate on which surface an insulating layer is formed.
In the flat-panel display device of the present invention, the back panel and the front panel can be bonded to each other in their circumferential portions with an adhesive or they can be bonded to each other with a combination of a frame made of an insulating rigid material such as glass or ceramic with an adhesive layer. When the frame and the adhesive layer are used in combination, a large distance between the back and display panels can be secured by selecting a proper height of the frame as compared with a case using an adhesive layer alone. While frit glass is generally used as an adhesive layer, a low-melting metal material having a melting point of 120 to 400xc2x0 C. may be used.
The low-melting metal material includes indium (In, melting point 157xc2x0 C.); an indium-gold-containing low-melting alloy; tin (Sn)-containing high-temperature solders such as Sn80Ag20 (melting point 220-370xc2x0 C.) and Sn95Cu5 (melting point 227-370xc2x0 C.); lead (Pb)-containing high-temperature solders such as Pb97.5Ag2.5 (melting point 304xc2x0 C.), Pb94.5Ag5.5 (melting point 304-365xc2x0 C.) and Pb97.5Ag10.5Sn1.0 (melting point 309xc2x0 C.); zinc (Zn)-containing high-temperature solders such as Zn95Al5 (melting point 380xc2x0 C.); tin-lead-containing standard solders such as Sn5Pb95 (melting point 300-314xc2x0 C.) and Sn2Pb98 (melting point 316-322xc2x0 C.); and soldering materials such as Au88Ga12 (melting point 381xc2x0 C.). All of the above subscript values show atomic %.
In the flat-panel display device of the present invention, when the back panel, the display panel and the frame are bonded, these members may be bonded at the same time, or one of the panels and the frame may be bonded in advance at a first step and the other panel may be bonded to the frame at a second step. When these three members are bonded at the same time or the other panel is bonded to the frame at the second step in a vacuum atmosphere, the space surrounded by the back panel, the display panel and the frame comes to be a vacuum concurrently with the bonding. Otherwise, the space surrounded by the back panel, the display panel and the frame may be evacuated to form a vacuum space after these three members are bonded. When the evacuation is carried out after the bonding, the atmosphere for the bonding may have atmospheric pressure or reduced pressure, and the gas constituting the atmosphere may be ambient atmosphere or an inert gas containing nitrogen gas or a gas coming under the group 0 of the periodic table (for example, Ar gas).
When the evacuation is carried out after the bonding, the evacuation can be carried out through a tip tube pre-connected to the back panel and/or the display panel. Typically, the tip tube is made of a glass tube and is bonded to a circumference of a through hole formed in an ineffective field of the back panel and/or the display panel with frit glass or the above low-melting metal material. After the space reaches a predetermined vacuum degree, the tip tube is sealed by thermal fusion. When the entire flat-panel display device is once heated and then temperature-decreased before the sealing, properly, a residual gas can be released into the space, and the residual gas can be removed out of the space by the evacuation.